Currently, there are different techniques for thermal printing, such as direct thermal printing or transfer printing, for example.
The common element for said thermal printing techniques is that they use a printing head, which, by means of heat, forms an image on a substrate, for example, a paper.
Direct printing is achieved by means of a chemical reaction of the components of the paper which is used, and which react with the heat of the printing head, the image on the paper thus being produced.
On the other hand, transfer printing is achieved by means of an ink which is in a polyester ribbon contacting the substrate, for example a paper or a plastic film. The ink used has a wax, resin or mixed base, according to the characteristics of the substrate and the durability desired for the printing. Thus, when the printing head is heated, the ink melts and when it contacts the cold substrate, the image is transferred to the mentioned substrate. The polyester ribbon having the ink is known as ribbon in the printing sector.
Reels suitable for the unwinding and winding of the ribbons which incorporate the ink for printing are used for both technologies, which reels are coupled in respective rotating shafts, which at least one of which is motorized or is driven.
The coupling of the reels in a corresponding rotating shaft becomes an object of interest in printing machines to facilitate the replacement and correct operation thereof, and different alternatives are known for the fixing of the reel in the rotating shaft.
As examples of such developments, a stop which must be placed at one end of the rotating shaft, more specifically at the base of the shaft, before placing the reel; and a tightening element, such as a nut, at the opposite end, which presses the reel against the stop, preventing its accidental removal, are currently used. A specific stop must be used for each reel width in order to ensure that the reel is kept coupled in a centred manner in the rotating shaft for a correct winding or unwinding, and to ensure a correct printing. This development necessarily involves the provision of several stops, in correspondence with the dimensions of the various reels, in addition to the use of a removable part, separable from the rotating shaft, formed by the tightening element or a similar element.
Rotating shafts are also known which incorporate complex expansible stop elements, and retaining means comprising sinkable tabs, which are not very satisfactory due to their high cost and complexity.
Therefore, a new simpler system and a device for the quick coupling of reels to a rotating shaft applicable to thermal transfer printing or direct thermal printing machines, which facilitates the replacement of the reels and which is more versatile, capable of adapting easily to different reel sizes without the need of having to replace the components thereof with others of different sizes, are necessary.